Glass Types for Building Envelope Products

There are typically four different glass types used in glazing products: From weakest to strongest they are: Annealed, Heat Strengthened, Tempered and Laminated.

1. Annealed glass is your basic non-impact glass type. It is used in applications where the required wind load is not so high and safety requirements are not a concern. When annealed glass breaks, it breaks in sharp chards.

2. Heat Strengthened glass is also a non-impact glass. It undergoes a “heat treatment” that increases it’s strength to twice that of annealed glass. It is used in similar applications to annealed glass but where the required wind loads are much higher. When heat strengthened glass breaks, it also breaks in chards.

3. Tempered glass is your basic impact glass. It undergoes a more aggressive “treatment” that increases it’s strength to four times that of annealed glass. It is used in “small missile” impact applications typically installed 30 feet or higher above ground and in safeguard applications. When tempered glass breaks, it breaks into very small cubes.

4. Laminated glass is your typical impact glass. It is a combination of two (usually) of the three previously mentioned glass types that are “laminated” together with an interlayer between them. It is typically used in “large missile” impact applications installed up to 30 feet above ground. When laminated glass breaks, it breaks based on it’s glass type make-up but is held in place by the interlayer…similar to a car’s windshield.

Rick DLG


News on Glass & Refractory World, week# 10

° RHI AG announced preliminary 2010 results pointing to over 23% increase in revenues (EBIT up almost 130%) vs. 2009, but still under ante-crysys figures. Results made possible thanks to an overall worldwide steel recovery of 15% with EU and USA over-performing. Cement and Glass still with subdued investments, except in China and Brazil.

° Pittsburgh Glass Works to reopen Evart plant; the plant was shut down two years ago and will begin restocking and rehiring later this month in preparation for a summer return to full manufacturing capacity. This is the result of increased demand for automotive glass products and will re-employ between 50 and 60 workers once fully operational.

° Financially troubled Zimglass fails to re-open; the company closed shop in August last year, resulting in about 472 workers placed on compulsory leave while they receive an allowance. The management had said they were closing shop to allow for the re-building of the only remaining furnace that was operational at the company. Now the company say financial problems had hindered them from re-building furnaces. Plans have been moved to next July for a possible revamping date.

° Ancai Hi-tech to Invest 460M Yuan In PV Glass Project. Henan Ancai Hi-Tech returned to profit in 2010, generating net profits of 32.61 million yuan, reports, citing a company filing. Color tube facilities in its colored glass factory ceased production, and related assets will be liquidated.

° German steelmaker ThyssenKrupp has announced that Kazakhstan’s first silicon metal plant Silicium Kazakhstan LLP has recently been commissioned in the province of Karaganda. Initially, the plant will produce silicon metal with one 12,500 metric ton furnace for customers mainly in Europe, Asia and the USA. A second furnace with the same capacity, already installed, is scheduled for startup in May 2011.

Low-e Coated Glass and the right usage

Here’s a short article which describes the right usage of Low-e coated glasses. Towards the last sentence of the article, it has been clearly stated that these glasses are used to prevent heat loss from the building in cold climate. But still the usage of these glasses have been mis-understood and are used in hot and humid climates, believing that they reduce the overall heat entering the building. True that they block long wave infra red radiation entering the building, just like they block them from leaving the building (which is why they are mostly used in cold climate).

Read the article on low-e coated glass here.

Designing Safely With Glass


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Here’s an interesting article by Rick De La Guardia on how to design safely with glass for today’s threats. This article was featured in US Glass Magazine. (Click on the article image to read more and download the entire edition)

News on Glass & Refractory World, week# 09

° Following previous announcements, Hindusthan National Glass (HNG) of India confirms to be in advanced talks to acquire two companies in Eastern Europe and Southeast Asia and MENA (Middle East and North Africa) regions. Due diligence processes will be completed within next few weeks.

° Indian Piramal Glass has announced investments for USD 57 million including expansion at its plant in Gujarat. Capacity addition will include 160 TPD in a greenfield project to be completed within 2012. Piramal will mostly focus on its cosmetics & perfumery containers business.

° UK-based speciality materials group Cookson Group Plc reports performance improvement in 2010 of its Ceramics division; a 52% increase in profits in the second half of 2010 has beer reached while refractory and foundry markets continued to recover. The business of Vesuvius and Foseco posts a trading profit of £90.6m., up from £59.5m. in H2 2009. End-markets have recovered strongly, but generally remain below pre-crisis levels.

Chemically Strengthened Glasses

Here’s an interesting find from This article claims about a new type of glass tempering, called Chemical Strengthening. It is also claimed in the article that these glasses are 6 to 8 times stronger than annealed glass, where as toughened glass is only 4 to 5 times strong. Most amazing fact is that these glasses could be cut after tempering unlike toughened glasses. However, the breakage pattern for these glasses remain almost the same as annealed glass, which obviously affects its acceptance in terms of safety.

Read the full article here.

Insulated Glass Units


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Insulated glass unit (IGU), also known as Double glazed unit (DGU) consists of two glass panes separated by dry air with an aluminum spacer. IGU has been in use in many countries since 1960s, except in the middle-east and Asia, … Continue reading

Is Glass Really A Green Building Material?

If somebody says that Glass is a green building material, the straight and honest answer would be a big No! Just because in many high rise green rated buildings, glass has been used extensively, it doesn’t make it a green product in itself. One might have encountered with many architects and glass industry professionals who bluntly promote glass as a green product, then why is this article contradicting that belief? Here is an explanation on why glass is not a green product by itself, but why it is essential for a green rated building. This article is in context of float glass only, which is the most widely used in buildings.

Glass could earn a few green points for the fact that it could be recycled. Broken pieces of glass are added along with the raw materials while glass is manufactured so as to bring down the boiling point and there by reduce the energy consumption. Also if the manufacturing facility is near to the building in construction, that could also fetch a few points for green rating, as the material is locally sourced. Local sourcing of material means less energy consumed for transporting the material.

Glass is extensively used in green buildings to harvest maximum light inside and to reduce energy consumption for internal lighting requirements. When more natural light enters a building, equal amount of heat also enters the building. 50% of the Visual Light Transmittance (VLT) is direct solar energy (ER or DET). So when you are asking for 100% light transmittance, you are getting 50% of heat along with it! If in a building, which is centrally air-conditioned, and if it is clear glass which is being extensively used, energy consumption for internal lighting might get reduced to a significant level, but at the same time energy consumption by the air-conditioner would be enormously escalated. This is where solar control and thermal insulating glasses play a major role.

Solar control glasses let in maximum light and also cuts DET down to a great level. Since 80 to 90% of heat entering a building is solar heat, maximum energy could be saved on lighting and air-conditioning. Apart from direct solar energy, non-solar energy or indirect energy, could also be controlled by using double glazed/ Isulated glass units(DGU / IGU), and thermal insulating glass. A DGU cuts down the heat entering a building due to conduction (glass is a good heat conductor) and convection. A thermal insulating or a low emissivity (Low-e) coated glass can reduce the non-solar heat by cutting down the transmittance of Long Wave Infra Red Radiation (LWIR). LWIR is emitted by objects like trees and furnitures during the night time, which absorb the Short Wave Infra Red Radiation (SWIR). In moderate to cold climate conditions, where heaters are used in buildings, it is better to go for a very low u-value glass, so as to prevent heat loss from the building. In tropical climates, it is better to have a moderate u-value range.

In short, it is not an isolated pane of glass that is green rated or that helps you gain green points, it is the configuration of glass units installed in your building, based on the window to wall ratio, orientation of the building, total glazing area, energy efficiency of the building, and hours of operation of the building occupants.

(Originally written for